I tried watching videos, now I'm stuck at Proboskus. he hits like a truck. I interrupt his torrent with my pet, than I run away from rain dance, but after a while he simply one-shots me with a melee attack and I don't know how to avoid that. could someone help me out?

EDIT: I'm a demo lock, using the beholder on this fight for it's interrupt.

I tried watching videos, now I'm stuck at Proboskus. he hits like a truck. I interrupt his torrent with my pet, than I run away from rain dance, but after a while he simply one-shots me with a melee attack and I don't know how to avoid that. could someone help me out?

EDIT: I'm a demo lock, using the beholder on this fight for it's interrupt.